A north finding system is used on equipment requiring north reference information such as antennae, projectile launchers and like equipment. The north finding system may feature a gyrocompassing arrangement. A system of the type contemplated is described in commonly assigned U.S. Pat. No. 4,686,771 issued on Aug. 18, 1957 to Thomas Beneventano, et al, and in commonly assigned U.S. application Ser. No. 327,874 filed on Mar. 23, 1989 by the aforenoted patentee.
In the aforenoted north finding systems an inertial platform includes an inertial instrument, i.e. gyroscope (gyro) mounted on an indexing pivot, which is utilized to implement gyrocompassing indexing positions. That is to say, the indexing pivot allows the gyro gimbal to be rotated to the various positions required for gyrocompassing. The pivot is equipped with a torquer to provide drive capability and an encoder for encoding angular position data.
Prior to the present invention electrical resolver arrangements were used to encode the angular position data of rotating members such as described above. In many applications such an arrangement is unsatisfactory since space, accuracy and resolution requirements can not be accommodated. Optical encoding arrangements using tracks and reader heads as does the present invention have been used, but have required many more tracks and reader heads then does the arrangement herein disclosed.
Accordingly the present invention accommodates encoding requirements by providing an optical encoding arrangement featuring an integrated optical disc having only three tracks and operable with a single reader head which interfaces with a computer through appropriate circuitry for providing absolute angle measurements.